Automated storage and retrieval systems are used to store and retrieve goods within a warehouse. The systems conventionally handles cases of goods loaded onto pallets. The loaded pallets are each stored and retrieved as single unit. Typical users of automated storage and retrieval systems include retailers storing inventory in a distribution center and manufacturers storing materials at a manufacturing plant.
The storage and retrieval system divides the warehouse into an induction area, a storage area and a discharge area. Loaded pallets are received or made up in the induction area and are then placed in the storage area for storage. Pallets are retrieved from the storage area and transported to the discharge area when the goods are needed.
The storage area includes a number of vertical storage racks spaced apart by vertical aisles. The storage racks have vertically spaced horizontal tiers with each tier having a number of storage bays spaced along the tier. Loaded pallets are placed in the storage bays for storage. The aisles are used to transport loaded pallets into and from the storage racks.
Automated vehicles traverse the aisles between storage racks. The vehicles transport loaded pallets from the induction area to the storage bays and from the storage bays to the discharge area. The pallets are carried on pallet supports. The vehicles also carry an auxiliary transfer vehicle that transfers pallets between the transport vehicle and designated storage bays. When the auxiliary transfer vehicle leaves the transport vehicle, it runs on tracks in the storage bays. The auxiliary transfer vehicle has a movable lift table that carries the pallet and can be raised or lowered to transfer pallets to and from a transfer vehicle or storage bay. The use of automated vehicles and auxiliary transfer vehicles to transfer pallets within the warehouse has increased the efficiency of known storage and retrieval systems.
In the simplest construction, a conventional storage area includes four parallel, spaced apart storage racks. The outermost racks are adjacent induction and discharge areas of the warehouse. Pallet elevators are located in the aisles adjacent the outermost racks. The elevators may access all bays in the tiers of the adjacent storage racks. Rails extend along each tier of aisles between the inner racks. Transfer cars run on the rails.
The movement of pallets into and from the storage area is controlled by an electronic inventory control system. The inventory control system tracks and maintains the locations of the pallets throughout the warehouse. The automated vehicles are directed by the inventory control system to store and retrieve pallets in specified storage bays. The movement of the automated vehicles and the storage and retrieval of pallets on the vehicles are directed by the inventory control system in conjunction with the sensors and control systems of the automated vehicles themselves. The inventory control system enables the storage and retrieval of pallets to be performed in accordance with known storage and retrieval algorithms or strategies, including, for example, first in-first out (FIFO) or last-in-first out (LIFO).
Conventional storage and retrieval systems are designed to store and retrieve large inventories of like goods. The goods normally are carried by a standard-size pallet having a footprint of 40 inches by 48 inches. The goods placed on a pallet typically are made up of a number of separate cases or boxes stacked to a maximum height of about 60 inches. The typical range in common case sizes will create pallet loads ranging from 4 cases per pallet for the largest cases to 96 cases per pallet for the smallest cases. The stack of cases is commonly wrapped with a plastic stretch wrap to hold the cases on the pallet and allow the loaded pallet to be handled as a single unitized load. A typical loaded pallet weighs between 1,000 pounds and 4,000 pounds. The storage racks and automated vehicles are designed to store and retrieve goods at the "pallet level", that is, to store and retrieve entire unitized pallets of goods.
Today's global marketplace has placed new demands on storage and retrieval systems. Businesses demand a more fluid supply chain to reduce cost. Modern business methods such as "just-in-time" purchasing practices have been developed to reduce transportation time and storage costs. These changes require warehouse orders of individual cases or limited numbers of cases. The growth of catalog shopping and electronic commerce has increased individual case shipments of customer orders from a centralized warehouse directly to the consumer, and decreased bulk shipments to retail stores or regional warehouses.
As a result, warehouses are shipping fewer goods at the pallet level and more goods at the case level. The amount of inventory kept on-hand is being reduced because there is less need to handle and store full pallet loads of identical goods. More goods are now being shipped in mixed pallets, that is, pallets containing cases of different articles within the same pallet load, or are being shipped in less-than-full pallet loads. For even smaller shipments, goods may be delivered in a number of separate, unbundled cases. Relatively small individual orders of assorted goods must be made up and shipped directly from the warehouse.
Conventional pallet storage and retrieval systems are unable to accommodate reduced inventories and individual order handling. These systems operate at the pallet level and cannot store and retrieve non-unitized cases of goods. Mixed pallets or unbundled deliveries of cases must be manually separated and loaded onto pallets before being stored in the warehouse. Individual orders of mixed cases must be manually made up from entire pallets of various cases retrieved from the storage racks. Mixed pallet orders also require manual makeup from retrieved pallets of the individual cases.
Consequently, users of conventional pallet storage and retrieval systems have been forced to add expensive manual labor or automated case handling systems to handle mixed pallets at both the receiving and discharge ends of the warehouse or to make up individual orders of various goods in the discharge area. Occasionally, conventional automated storage and retrieval systems have been abandoned altogether because of their inability to store and retrieve goods at "less-than-pallet" level.
Thus, there is a need for an improved storage and retrieval system for storing and retrieving goods in a warehouse. The improved system should be capable of handling both conventional palletized loads and separate cases of goods. The improved system should automatically store individual cases of goods received at an induction area and deliver selected individual cases of goods to a discharge area. The improved system should store the cases in conventional storage racks and deliver made up orders made of different cases of goods from the storage racks to the discharge area using conventional automated vehicles. The improved system should eliminate the need to invest in additional automated transport and handling equipment specifically designed to handle only smaller case-sized articles.